1. Field of the Invention
The present invention relates to a semiconductor device and an electric power conversion system using the semiconductor device. In particular the present invention relates to a semiconductor device which is suitable for an Insulated Gate Bipolar Transistor (hereinafter referred to as IGBT) having a trench insulated gate structure, and to an electric power conversion system using the semiconductor device.
2. Description of the Related Art
The IGBT is a switching element that controls electric current flowing between the collector electrode and the emitter electrode by a voltage applied to the gate electrode. A power controlled by the IGBT ranges from tens of watts to several hundred thousand watts. In addition, the switching frequency ranges from tens of Hertz to several hundred thousand Hertz. Due to these wide ranges, the IGBT is widely used in small electric appliances such as household air conditioners and electronic ovens, as well as in large electric appliances like inverters used in railroad and steel works.
For improving the efficiency of these electric appliances, reducing loss is a requirement to the IGBT. In other words, reducing conduction loss and switching loss is required to the IGBT. In addition, in order to prevent problems such as EMC noise and mal-function, electric breakdown of a motor etc., it is also required to be able to control dv/dt, the rate of change of output voltage, in accordance with a specification of an application.
A patent document JP 2000-307116 A (referred to as Patent Document 1 hereinafter) discloses a technique of producing an IGBT by arranging trench insulated gates at different intervals, forming a channel on a side where a trench distance is smaller, and forming a p-type well layer on a side where a trench distance is larger. This technique achieves an IGBT having input capacitance of the gate lowered, low switching loss, low on-state voltage and low saturation current, without decrease in a withstand voltage.
In addition, another patent document JP 2005-327806 A (referred to as Patent Document 2 hereinafter) discloses a technique for implementing an IGBT having a small gate-collector capacitance (GC capacitance), a large capacitor ratio between gate-emitter capacitance (GE capacitance) and the GC capacitance, a high switching speed, a low switching loss, and a high injection coefficient of on-state by employing a structure without a floating well.
However, in a conventional IGBT described in Patent Document 1, controllability of dv/dt of the output voltage of the IGBT when turned on, or dv/dt of the voltage of a diode (free-wheeling diodes) of arms may decrease when using the IGBT in an electric power conversion system.
In addition, forming a wide trench causes a high step portion, and the high step may cause difficulty in manufacturing and designs.
Further, when the production method described in Patent Document 2 is used, there may be a case where a crystal defect occurs due to epitaxial growth covering the insulating film, and the crystal defect causes a large leakage current. Still further, since the number of forming processes of the substrate is increased, the cost of the substrate may be increased.